1. Field of the Invention
The present invention relates to a light source apparatus for an endoscope, which is designed to be capable of automatic exposure control when a photograph is to be taken through the endoscope.
2. Description of the Background and Relevant Materials
To effect automatic exposure control when a photograph is to be taken through an endoscope, it is necessary to change a set reference that is used to determine a correct exposure, that is, an exposure index that is used in automatic exposure control, in accordance with various conditions, for example, the type of endoscope, the magnification of a photographic adapter and the sensitivity of a film, which are employed in the photographing operation.
To meet this need, a typical conventional light source apparatus for an endoscope has heretofore been arranged such that an optimal one of several different exposure indexes can be selected by a manual operation in accordance with a combination of various conditions.
However, the selection of an optimal exposure index in accordance with each particular combination of various conditions necessitates referring to an instruction manual, for example. Therefore, no rapid setting of an exposure index can be performed, and a setting error is likely to occur. If erroneous setting is made, the whole film will be over- or under-exposed.
In addition, in the conventional light source apparatus, the adjustable range of exposure indexes is fixed. Accordingly, when a new type of endoscope or a photographic adapter whose magnification is quite different from those of ordinary ones appears, or when a film whose sensitivity is markedly different from those of ordinary ones is used, an exposure index which is appropriate therefor may be out of the adjustable range. In such a case, it is impossible to set an appropriate exposure index, and the whole film will therefore be over- or under-exposed.